Hematocrit

This is the percent of the blood that is red blood cells. It is a ratio. It tells if there are enough red blood cells in your blood. The hematocrit is usually done by placing the blood in a tube and spinning the tube in a centrifuge. This separates the solid parts of the blood from the liquid plasma.

When heparinized blood (heparin is an anticoagulant) is centrifuged, the red blood cells become packed at the bottom of the tube, while the plasma is left at the top as a clear liquid. The ratio of the volume of packed red cells to the total blood volume is called the hematocrit.